This invention relates to a thermal analyzer which includes a gas chromatograph for analyzing a gas generated from a sample placed in the thermal analyzer, and particularly a thermal analyzer equipped with a scavenging unit for scavenging the generated gas.
Prior art thermal analyzers which comprise a gas chromatograph (hereinafter called a GC) connected to a thermal analyzer are described as follows.
An exemplary prior art 1, Wiedemann, et al. (Thermal themal analysis Vol. 1, Academic, New York 1969, p. 229) discloses a connection of a thermal gravimetric analyzer (hereinafter called as TG) and a GC. Generated gas from the TG is introduced to an aggregate tube, which is called a "sample loop" with the aid of a carrier gas, and then the gas generated in the aggregate tube is introduced into the GC by switching the flow path via a sampling valve.
A prior art No. 2, J. H. Slaghuis, et al. (Thermochimica Act a, Vol. 175, 1991, p. 135), discloses that the generated gas from a TG is transmitted to a switching valve with the aid of a carrier gas, and then a sample which is obtained by sampling from a number of aggregate tubes into which the gas is fed is finally introduced into a GC.
According to a prior art No. 3, which is disclosed in the "SHIMAZ KAGAKU KIKAI News" Vol. 12, No. 10, 1971, p. 5, a gas is generated in a thermal analyzer and transmitted with the aid of a carrier gas and scavenged in a multiple number of aggregate tubes with a self-closing valve through a joint. Through another joint which is connected to each aggregate tube, the gas in the aggregate tube is introduced into a GC.
Acccording to a prior art No. 4, which is disclosed in the catalogue of Shimaz thermogranimetry gas chromatography mass spectrometer TGA-GCMS-QP1000EX, gas from a TG is transmitted with the aid of a carrier gas and scavenged into a trap (scavenger) via a cock, and then the gas which is in the trap is introduced into a CG by switching the cock.
According to a prior art No. 5, which is disclosed by YAMAHA et al. (Proc. 4th ICTA Conf. I. Buzas u. ed., Vol. 3 Heyden, London, 1975, p. 1029), gas from inside a differential thermal analyzer (hereinafter abbreviated as DTA) is introduced with the aid of a carrier gas from DTA into a scavenger, and then the gas is introduced into a GC by turning the scavenger off and sending it to the GC.
Generally speaking, the gas generated from the sample set in the thermal analyzer is generated due to a thermal decomposition and/or elimination reaction in relation to temperature rise, and such reaction itself is known to change according to measuring conditions (for example, programming rate, gas in the atmosphere, etc.) The flow rate of carrier gas used for the atmosphere control is also one of the measuring conditions. Accordingly, the flow rate of carrier gas should be given the same value for observing the difference etc. in reaction between samples.
The volume of the sample in case of analysis in a GC should be also appropriate. Accordingly, the volume of the gas to be generated in the thermal analyzer should also be appropriate in case of analyzing such gas which is to be introduced into the GC. In the prior art, sampling of such gas in analysis in a GC is made transmitting the gas with the aid of a carrier gas from the thermal analyzer.
In the prior art No. 1, No. 2, and No. 3, the gas is introduced into the aggregate tube with a predetermined capacity, and in the prior art No. 4 and No. 5, into a scavenger (absorbent, cold trap, or combination of both). Since the flow of carrier gas is constant, the sampling volume of the gas to be analyzed is determined on the basis of the capacity of the aggregate tube in case of sampling with an aggregate tube, or on the basis of the duration of time in case of sampling with a scavenger. Accordingly, in the transmitting method with carrier gas there exists a drawback that the range over which the best sampling in a GC can be done is narrow, as shown below.
In the use of an aggregate tube, the capacity for the gas to be sampled becomes very small if the speed of gas generation from the sample is very low, and sometimes a drawback exists that it can not be detected in a GC. On the contrary, in case that the capacity of the aggregate tube is increased for the purpose of increasing the gas generation for sampling above, the dead volume in injection to a GC increases, and therefore its isolation at the GC becomes worse in effect and becomes undetectable in practice.
In the use of the scavenger, the duration of time can be longer for scavenging gas in case of the slower gas generation. On the contrary, in case that the gas generation is very speedy, the sampling volume of the gas above becomes too large, and therefore it becomes not analyzable because of too much gas in the sampling hood in the analyzing column, which is another drawback. Moreover, there exists the following drawback in the prior art of transmitting sample gas with the aid of a carrier gas.
In the thermal decomposition reaction where gas generates, there exists often the case that the reaction mechanism becomes different in each stage of reaction, initiation, mature and ending. And in the case of plastic materials etc., a microelement of an addition agent, or a monomer which is not reacted yet, etc., may be present before the thermal decomposition. Accordingly, it is important to effect sampling and to analyze the gas at each stage of the reaction. In such a case above, a multiple number of aggregate tubes or scavengers is useful in sequential sampling at each stage of the reaction. As seen in the prior art No. 2 or No. 3, with the use of a switching valve or switching joint, the flow of the generation gas from the thermal analyzer is switched into specific aggregate tubes for sampling. In the case that the generation gas is transmitted in the prior art, the switching valve etc. for switching the flow of the gas above should be placed in between the thermal analyzer and the aggregate tubes, etc.
But there exists the following problem in case that a switching valve, etc. is placed in a flow path. It often occurs that the boiling point of the generation gas in thermal discomposition, etc. is higher than ordinary temperature. Therefore, the temperature of the flow path up to the aggregate tube is usually kept at, for example, 200.degree. C., and the flow path is at a pressure higher than atmospheric pressure. The switching valve made of a metal such as stainless steel is usually the most appropriate since it is suitable for heat-proof and pressure-proof conditions. But, there is possibility that the generation gas above is trapped at the surface of the metal due to absorption or is exposed to a second order reaction. Valves made of inactivated glass in relation to the generation gas have a problem of pressure strength and valves made of plastic materials such as Teflon.TM. have problems of heat strength, of gas generation from such materials themselves, and/or of sample absorption.
This is to say, since sampling of the gas for analysis is made by using a carrier gas from a thermal analyzer in the prior art, there exists a difficulty in sampling an appropriate volume of gas in a GC for the measurement, and a problem that the materials of the switching valves, etc. affects to the measurement in case of multiple times of sampling of the gas above at multiple stages of reaction.
The object of this invention for the purpose of solving problems in prior art, is not to use a carrier gas for sampling of the gas above and therefore to carry out the sampling procedure with no relation to the flow of the carrier gas, and to obtain such constitution of a gas scavenging unit that a switching valve has no effect on the measurement even in the case of multiple stages of sampling.